(1) Field of the Invention
This invention is related to the means of attachment between the spoke and the rim of a vehicle wheel and between the spoke and the hub of a vehicle wheel. This invention is particularly related to the connection of a spoke with a rim structure having a “double-wall” construction with an unpierced tire bed wall for tubeless tire applications.
(2) Description of the Related Art
Bicycle wheel rims have historically been constructed to accept pneumatic tires that are designed to work in conjunction with an inner tube. This is the standard of the industry and is the arrangement that we are all familiar with. In such a prior art configuration, the rim's tire bed includes a through-hole that is drilled through for passage of the spoke nipple. In a rim of “single-wall” construction, the tire bed and the spoke bed are shared such that the spoke nipple bears directly against the rim's tire bed. In a rim of “double-wall” construction, the rim has two lateral walls, a tire bed wall and a spoke bed wall, usually with a radial gap or cavity therebetween. The rim is drilled through both walls, piercing both the tire bed and the spoke bed walls, with the spoke bed recessed below the tire bed to accept the spoke nipples. Generally, the spoke is presented through the spoke bed from the inside diameter of the rim and the spoke nipple is presented for attachment to the spoke through the tire bed and from the outside diameter of the rim. With single-wall or double-wall rim constructions, a rim strip is utilized to protect the inner tube from the sharp edges associated with the holes in the tire bed wall and/or with the spoke nipples. With rims of double-wall construction, the rim strip also serves to prevent the inner tube from extruding through the drilled access openings in the tire bed.
With the recent advent of tubeless tire technology, where the conventional inner tube is eliminated and the tire's beads are sealed directly against the rim, it is desirable that the tire bed wall be sealed and airtight to prevent air leakage from the tire cavity. This typically involves a rim of double-wall construction where the tire bed is sealed while the spoke bed is then adapted to accept the spokes. One preferable method for sealing the tire bed is to eliminate the aforementioned spoke access holes in the tire bed. If the tire bed is not pierced for the spokes, then the only hole through the tire bed will be for the tire inflation valve, which may be constructed of rubber and is relatively easy to seal against the tire bed. An example of such a tubeless arrangement is outlined by Lacombe et al. in U.S. Pat. No. 6,443,533, where the tire bed remains unpierced and the spoke bed includes extruded spoke holes that are directly threaded with internal threads to accept special externally threaded spoke nipples.
Reference is also made to prior art UK Patent Application GB2479870A by Jonathan Thulbon. Thulbon shows his spoke (3) connected to his rim (4) by eyelets (7). This eyelet is a one-piece element with slots (74) to provide flexure for installation with his rim. Thulbon's arrangement has several shortcomings: Firstly, the fact that his single-piece eyelet must flex for installation requires that the material of his eyelet be of relatively flexible and ductile material, such as unreinforced plastic. However, such material generally has low strength in comparison to stronger materials that are more rigid and less ductile, such as metals or fiber-reinforced plastics that would not be able to flex as Thurbon requires. Since spoke tension forces exert a very high stress at its connection to the rim, the weaker material of the Thulbon eyelet results in a relatively weak spoke connection that may also be more prone to flex and creep. Second, since Thulbon's eyelet is of one-piece design, the entire eyelet must be inserted at one time. This simultaneous installation, as well as accommodation for his flexure, places severe geometry restriction on his eyelet. As such, Thulbon's design is limited to a relatively shallow depth of lateral overlap and engagement between his eyelet and his rim, thus increasing stresses at this interface and further weakening his spoke connection. Thirdly, the overlie engagement between Thulbon's spoke nipple and eyelet is located inwardly from the outboard surface of his spoke bed, which requires that his eyelet include longitudinally outward extension portions that surround the head of his nipple to engage his rim. These extension portions require that the corresponding hole in his rim be significantly larger than the head of his spoke nipple. This oversized hole serves to further weaken his rim in this highly-loaded area. Fourthly, these extension portions also serve to laterally offset the overlie engagement between his rim and eyelet from the overlie engagement between his eyelet and nipple. This offset places additional tensile and bending stress on the eyelet due to spoke tension forces, further weakening his spoke connection. Fifthly, Thulbon does not contemplate a longitudinal engagement between his spoke and eyelet and instead utilizes only a single overlie engagement at a single longitudinal location. Such a single overlie engagement requires a very large laterally projected area of overlie to resist spoke tension loads, which results in a larger eyelet and a correspondingly larger hole in his rim.